As disclosed in Patent Literature 1, a flow rate control apparatus is equipped with a valve provided on a flow path, a flow rate sensor provided on an upstream side of the valve and a valve control part configured to control an opening position of the valve so that a measurement flow rate value measured by the flow rate sensor follows the set flow rate value, and an object thereof is to continuously stabilize the flow rate in a downstream side of the flow rate control apparatus.
By the way, in the case where there occurs a pressure fluctuation in a flow path in an upstream side of the valve, it becomes a disturbance in controlling. Therefore, an opening position of the valve is changed due to the control performed by the valve control part. As a result of this, the flow rate in the downstream side of the valve may deviate from the set flow rate value in some cases.
That is, despite the flow rate in the downstream side of the valve, which is a target for the flow rate desired to be actually stabilized, is preciously stable, a stable flow rate control state is impaired due to the pressure fluctuation in the upstream side of the valve where there is no problem even though the flow rate is disturbed.
In order to solve this problem, in Patent Literature 1, a pressure sensor for detecting the pressure fluctuation is previously provided in the upstream side of the valve and the flow rate sensor, and based on the pressure detected by this pressure sensor, a control coefficient such as PID system coefficient is appropriately changed and it is configured so that the flow rate in the downstream side of the valve can be kept at the set flow rate value constantly.
By the way, a cheaper version omitting the pressure sensor which is not an essential component for the flow rate control apparatus in some applications is required in some cases, and there has been a demand for stabilizing the flow rate in the downstream side of the valve with an accuracy not at all inferior to the flow rate control apparatus described in Patent Literature 1 even without the pressure sensor.